Increasing demand in energy requirement, associated with EU regulations, are compelling the attention on alternate fuels. The change from a fossil fuel to a biofuel is being highly associated with the waste management technologies, with significant environmental and economic benefits, by valorising specific waste streams. Certain types of wastes might present significant organic oil and fat contents, such as those originated in waste water treatment plants (WWTP), generally known as brown grease, grease traps, from WWTP of several food and dairy industries and from processing animal products. Such wastes are difficult to treat, namely due to its heterogeneous composition, presenting high levels of solids, water and free fatty acids (FFA) and usually end up being landfilled, although waste management policies discourages such conduction, or directed to composting plants.
In addition, oils and fats with high FFA content are not suitable to be used directly in the conventional biofuel production process. FFA is undesirable during the alkali transesterification process due to the formation of soap, yield loss, and increased difficulty in product separation. Waste streams of organic oils and fats that are recovered from waste water treatment plants (WWTP), generally known as brown grease, grease traps and from WWTP of several food and dairy industries can contain considerable amounts of FFA. Depending on the source of the raw material, FFA content may be between 0% (w/w) and 100% (w/w), nevertheless the referred waste streams of organic oils and fats from waste water treatment plants (WWTP), generally known as brown grease, grease traps and from WWTP of several food and dairy industries generally have FFA content higher than 50% (w/w).
The present invention disclosures a process to extract and valorise FFA from waste streams containing potentially high content of organic oils and/or fats, such as brown grease, oils/fats from grease traps or from WWTP of food industries, which, because of their high content of FFA, would otherwise not be valorised, being mainly landfilled, with the associated negative environmental impact. This new process of waste treatment is a two stage process, where the first stage consists in a physical treatment to extract and recover the oils and/or fats from the waste stream, and the second stage is a glycerolysis reaction where the FFA present in the oils and/or fats, recovered in the first stage, is transformed in a glycerol ester.
EP 1051386B1 discloses a process for the production of monoglycerides by glycerolysis of methyl ester derived from animal or vegetable fat and oils.
EP0334154 discloses FFA esterification with sulphuric acid, toluene sulphonic acid, cholorosulfonic acid and methylsulphonic acids in alcohol, while U.S. Pat. No. 6,965,044 discloses the esterification of acid oils or fats with sulphuric acid along with methanol.
Further methods for esterification of FFA using different type of solid catalyst are described, such as ion exchange resins (EP20070254389, EP1921131 and U.S. Pat. No. 7,256,301). US2011/0105775A1 discloses the use of an acidic solid catalyst dissolved in an alcohol.